US3300678A - Traveling wave tube with plural pole piece assemblies defining a vacuum sealed tube body and particular collector structure - Google Patents

Description

1 8 t 7 Be 6, mm m i 3 u s mm 3 e h Rs 0 T5 N. E. SWENSEN L POLE PIECE ASSEMBLIES DEFINING Jan. 24, 1967 TRAVELING WAVE TUBE WITH PLURA A VACUUM SEALED TUBE BODY AND PARTICULAR COLLEG Filed May 15', 1963 Jan. 24, 1967 N. E. SWENSEN 3,300,678

TRAVELING WAVE TUBE WITH PLURAL POLE PIECE ASSEMBLIES DEFINING A VACUUM SEALED TUBE BODY AND PARTICULAR COLLECTOR STRUCTURE Filed May 15, 1963 3 Sheets-Sheet 2 N. E. SWENSEN 3,300,678

PLURAL POLE PIECE ASSEMBLIES DEFINING A VACUUM SEALED TUBE BODY AND PARTICULAR COLLECTOR STRUCTURE 3 Sheets-Sheet 5 Jan. 24, 1967 TRAVELING WAVE TUBE WITH Filed May 15, 1963 .zwrs/vrae jVbRMA/V E SWE/s/SEN,

5 Ms AfrwQA/Eyf Mad m United States Patent ()fiice 3,300,678 Patented Jan. 24, 1967 fornia Filed May 15, 1963, Ser. No. 280,542 4 Claims. (Cl. 315-3.5)

This invention relates to traveling-wave tubes, and more particularly to a periodic permanent magnetic focusingwave tube.

A traveling-wave tube is a radio-frequency amplifier. All traveling-wave tubes have an input of radio-frequency energy, a slow wave device and an output for the amplified energy. An electron gun shoots an electron beam through the slow wave device into a collector. When the velocity of the electrons from the gun is somewhat greater than the axial velocity of the radio-frequency Wave as they pass through the slow wave device, an interaction takes place which delivers energy to the wave, causing it to then become larger as it approaches the output, resulting in amplification.

The electron beam from the gun is focused and centered in the slow wave device by a magnetic field. While earlier magnetic focusing fields were produced with coils, they were heavy, required high power and radiated external flux which interfered with external circuit operations. These later were replaced with periodic permanent magnetic focusing magnets. Since a uniform magnetic field was needed for continuous focusing along the beam, pole pieces were positioned along the electron beam path and were used to form the magnetic field. Their energy was provided by magnets. The pole pieces were never split as a uniform field was needed. The magnets, however, could be split because the nonnniformity magnetizing characteristics of magnets were compensated for by the pole pieces.

Because of the larger input and output connections, the pole pieces must be assembled over the vacuum housing of the slow wave device before the device, including the electron gun and collector, has been evacuated. The pole pieces must be positioned around the tube and carried thereby. With use of larger currents and, because the radio-frequency energy becomes amplified before leaving the tube, the collector and the output apparatus must be larger for higher power capacities. However, because the electron gun end of the vacuum envelope is bigger than the slow wave portion which usually contains only a helix conductor, the pole pieces must be inserted over the tube envelope from the other end containing the collector and output apparatus. This limits the collector and output in size to no bigger than the pole pieces which must be inserted thereon, severely limiting the output capability of the tube.

Another principal disadvantage of prior art travelingwave tubes is that in their fabrication the vacuum assembly must be complete before testing for faulty parts. At this time, when a failure occurs, the whole tube must be scrapped.

The traveling-wave tube comprising the present invention utilizes small subassembly sections, each of which may be inspected and vacuum tested before being added to the assembly. Instead of inserting pole pieces over a vacuum envelope as was previously done, the pole pieces are welded together to become part of the vacuum envelope. Since periodic magnetic focusing is used for continuously focusing the electron beam along its path within the slow wave section, the tube slow wave section may be made as long or as short as desired for any particular application, simply by adding or removing pole piece assemblies. The pole piece assemblies are welded together to form an input section and an output section to which the electron gun and collector assemblies, respectively, are added. Helix conductors of desired length are welded to the input and output connectors, respectively, and grounded to the pole pieces where the input and output sections are joined. This makes the assembly of the helix in the slow wave section much easier and simpler than trying to attach both ends of the helix to the input and output connectors without varying the pitch of the helix.

The traveling-wave tube comprising the present invention has many advantages and improvements over previous devices, one of them being that each part may be checked for flaws before its assembly, and those failing to meet with predetermined requirements may be discarded and replaced with another part. In this manner each part that is discarded for fault is a small inexpensive part and does not cost as much to discard as a larger assembly or a complete tube.

Another advantage is that an arrangement of periodic permanent magnetic focusing is made which allows for unlimited size of collector and output matched portions so that they may have a greater energy-carrying capacity.

Another improvement is that of providing for brazed subassembly sections that can be mated to each other by localized welding or brazing in an area away from the alignment portion of the subassembly so that welding or brazing heat will not cause warpage or misalignment of parts.

Another improvement lies in the novel magnetic pole pieces which form sections of the vacuum envelope rather than be assembled over an envelope.

Another improvement lies in the provision of a severed helix concept wherein two spaced helix coils in separate subassemblies are mated to the input or output connections where they terminate in a smooth transition.

Another improvement lies in a novel collector arrangement wheren the vacuum pump is shielded from electron impingement of the electron beam.

These and other objects of the present invention will become more apparent as a description of the invention proceeds with reference to the drawings, wherein:

FIGURE 1 is a schematic diagram of a conventional traveling-wave tube;

FIGURE 2 is an elevational view, with parts broken away to better illustrate the features of a traveling-wave tube utilizing the features of the present invention;

4 FIGURE 3 is a sectional view of the barrel assembly input section;

FIGURE 4 is a sectional view of the barrel assembly output section;

FIGURE 5 is an end view, taken along the lines 55 of FIGURE 2;

FIGURE 6 is an elevational view, partly in section, of a pole piece assembly; and

FIGURE 7 is a perspective view of the pole piece assembly.

The essential elements of a traveling-wave tube are shown in FIGURE 1. Here is shown an electron gun 10, slow wave device 30 and beam collector 14. The electron gun consists of a heater 16, emissive cathode 18, beam-forming electrode 20 and accelerating anode 22, within an evacuated envelope 24. The heater 16 and cathode 18, connected to power supply 26, cause the emission of electrons which are formed into a beam by beamforming electrode 20. Both the accelerating anode 22 and the beam collector 14 are connected at a higher potential, as illustrated by power supplies 28 and 28a.

The electron gun 10 produces a cathode-ray beam having a velocity typically proportional to a potential of 1500 volts. This beam passes through a long closely wound helix 30 positioned between the gun and collector 14 in the envelope 24. An axial magnetic focusing field is provided by focusing coils 32 to aid in maintaining the beam diameter small and to guide the beam through the center of helix 30. The signal to be amplified is applied, such as by coax 34, to the end of the helix adjacent to the electron gun 10. Under appropriate operating conditions, an amplified signal then appears at the other end of the helix, such as from coax 36. While coax input and output arrangements are illustrated, waveguide connections may be used, as desired.

The input signal produces a wave that propagates along the helix with the production of a traveling axial electrostatic field inside the helix. The velocity with which this field travels corresponds to propagation around the turnsof the helix at nearly the velocity of light. Since the helix pitch, or axial length of one turn, is less than its circumference, the axial velocity is less. The axial velocity is approximately the velocity of light multiplied by the ratio of helix pitch to helix circumference. When the velocity of the electrons of the electron beam from gun 10 traveling through the helix is slightly but uncritically greater than the axial velocity of the wave on the helix, an interaction takes place between the moving axial electrostatic field of the helix wave and the moving electrons. This interaction is of such a character that on the average, the electrons deliver energy to the wave. This causes the wave to become larger as it approaches the output end of the helix, resulting in amplification.

The power-handling ability of the traveling-wave tube can be limited by the amount of heat that may be dissipated from the helix. The helix becomes increasingly hotter as amplification occurs, since electrons from the beam impinge upon it, particularly if the tube is of an appreciable length. As the electrons from the beam impinge upon the helix, they give up energy in the form of heat, raising the temperature of the helix. It thus becomes very important that this bombardment of electrons onto the helix be reduced to 'a minimum, particularly when the tube has a high amplification characteristic. The electron beam may be confined magnetically by employing a sinusoidally varying magnetic field, and because of this field pattern, such tubes are usually referred to as periodically focused traveling-wave tubes. Instead of a single electromagnetic focusing coil, a plurality of ring-shaped magnets and pole pieces are disposed with adjacent poles of magnets of the same polarity; that is, the adjacent magnet faces are of the same polarity. The actual field of the magnetic structure coin cides with the axis of the slow wave structure; that is, the helix of the traveling-wave tube (TWT).

Such a tube is shown in FIGURE 2. In this view, the gun assembly 38 is shown on the left. Since this gun assembly is illustrative of any of the conventional electron guns readily available, its details are not now explained, its function being to transmit an electron beam through the slow wave structure to the right. Its essential elements are the gun 10, including heater 16, emissive cathode 18, beam-forming electrode 20 and accelerating anode 22. The electrons emitted from cathode 18 are formed into a beam by electrode 20 and pass through aperture 40 in anode 22. The anode support ring 42 supports the gun assembly and is secured preferably by heliarc welding to gun alignment flange 44. The gun alignment flange 44 is adapted to be positioned over input matched assembly collar 46 and moved about until the electron gun is axially centered and then the flange 44 is welded thereto. It should be noted here that the welding is about the periphery so as not to heat any alignment devices that may be used, thus causing them to warp or expand and thereby making the alignment difiicult.

The barrel assembly input section 54 consisting of a cylinder 48 with spaced radially extending flanges or pole pieces 50 extends axially from the assembly collar 46. Cylinder 48, in reality, and pole pieces 50, in reality, consist of a multiple of separate pieces and of different types of materials all welded together into a unitary piece, as will be explained and shown in detail hereinafter. Positioned between pole pieces 50 are annular or donutshaped magnets 52. Since these magnets are installed after the final welding and outgassing process so that their magnetic properties will not be destroyed by the heat required to outgas the tube, these magnets are split into half-circles for ease of insertion. The faces or sides of these magnets abutting opposite sides of their associated pole piece are of the same magnetic polarity, so as to magnetize the pole piece with a single polarity. Alternate pole pieces are magnetized with the opposite polarity. A predetermined number of pole pieces forming a predetermined length of cylinder 43 may be used in constructing the barrel assembly input 54- (the left half of the Wave tube illustrated).

Mounted within this left half or barrel assembly input 54 is a helix assembly consisting of a helix 30 centrally positioned by circu'mferentially spaced insulating rods, such as alumina rods 5s, 58, 60. These rods are made of suitably electrical insulating material capable of withstanding relatively high temperatures. Sapphire and quartz rods also may be used, if desired. Suitable locating means, such as sleeve 62, surrounds the rods and serves to maintain the same circumferentially spaced. This sleeve extends substantially the entire length of the rods and may be a metallic member, such as molybdenum. The rods and locating sleeve provide a good heat conduction path to cylinder 48 from the helix 3%), which is the waveretarding conduct-or in this embodiment.

Helix 30 terminates slightly spaced from the inner end 66 of the barrel assembly input 54 and is electrically connected to the barrel by means of metal ribbon straps 64 which are connected to cylinder 48. Coupler 68 provides means for coupling energy onto the helix 30. This coupler is adapted for coaxial connection and consists of an outer sleeve '70 with a ceramic spacer 72 welded thereto with a metal-ceramic braze, in accordance with wellknown techniques. A central pin 74 extends through the match ceramic spacer and is connected to the innermost end 76 of helix 30.

The barrel assembly output section 80 is constructed in a manner similar to that of barrel assembly input 54 and for this reason its description is not believed to be necessary. Like numerals followed by a small letter a represent parts similar to those in the input section 54. Out-put coupler 68a provides means for coupling energy from helix 30a and consists of a sleeve 70a, ceramic spacer 72a. A threaded match adapter 82a and coax connector 84a complete the connection with a coax conductor, not shown. The assembly of the tube is completed by mating the last adjacent pole pieces of input section 54 and output section 80 and heliarc welding them together at their outer peripheries into one unitary piece. It should be noted that although helixes 30' and 30a are in alignment, they do not connect directly but connect through straps 64-, 64a which are integrally connected through pole pieces 50b and 50c, in turn welded together as an integral unit.

A terminal collar 86 is at the opposite end of the barrel assembly output section 8011. This collar has connected thereto a collector assembly 88 and vacuum pump assembly 90 through ceramic spacer 92. This ceramic spacer consists of a cylindrical ring 94 bonded between metallic rings 96, 98. Metal ring 98 is then bonded to terminal collar 86. Collector assembly 88 consists of beam collector 14 having connecting rings 100 and 102 bonded thereto. This collector has an aperture 104 and a blocking window 106 having aperture 108 therein through which the electron beam passes. The beam impinges upon collector plug 110 which in turn is electrically connected to ring 102 through strap for connection to external circuitry. The vacuum pump assembly 90 includes an ion pump magnet 112 and ion pump assembly 114. This assembly is connected to collector assembly 88 through ring 116. Passageway 118 in collector plug 110 permits the pump to continuously maintain a vacuum within the traveling-wave tube, while blocking window 106 and collector plug 110 blocking the electron stream from the pumping apparatus. Blocking window 106 further serves as an extra secondary trapping of the electrons. The collector assembly is aligned with the electron beam by proper lateral movement of the assembly prior to the welding of ring 100 to ring 96. This is the last weld in the assembly.

Reference is now made to FIGURE 3 which shows a sectional view of barrel assembly input 54. Here it can be seen that cylinder 48 and pole pieces 50 consist of a plurality of pole piece assemblies 120. These assemblies consist of a sleeve 122 interconnecting spaced pole pieces 5% and 500. Pole piece 5% of one assembly abutting and welded to pole piece 500 of another assembly comprise an integral pole piece 50, as shown in FIGURE 2. This will be described in greater detail in connection with FIGURES 6 and 7, it being sufiicient at this time to state that cylinder 48 consists of a plurality of pole piece assemblies 120 with pole pieces 50!) and 50c thereof welded together in a vacuum-tight relationship, such as by heliarc welding for example. This bonding is done about the periphery such that the bonding heat does not warp or distort the alignment apparatus used in the assembly thereof. Coupler 68 consists of sleeve 70 having a ceramic spacer 72 spacing central pin 74 from sleeve 70. This spacer is bonded in vacuum-tight relationship to the sleeve 70 and to the pin 74. Inner sleeve wall 124 is sufficiently spaced from pin 74 to be insulated therefrom. An assembly cover 62 serves as a locating means for positioning helix 30 within the cylinder 48. Rods 56 and 60, and 58 not shown, center the helix within this cover 62. After the helix has been inserted within the cylinder, its innermost end 76 is carefully mated with pin 74 so as to provide for a smooth electrical transition therebetween and the connection is then bonded. After this connection has been made, collar 126, against which cover 62 abuts, is then positioned and welded on assembly collar 46. Thereafter helix 30 is cut back to desired length at end 66 of input section 54. Collar 128 is then positioned in abutment with cover 62, and straps 64 are welded between the helix 30 and the innermost pole piece 50b. A similar assembly of the helix in the output section, using a severed helix technique, makes the mating of the helix ends with the input and output connecting pins much easier than attempting to construct a helix of predetermined pitch of exactly the right length to be mated between the input and output pins as was formerly done. As can be seen by the clearance gap 128, the gun alignment flange 44, after gun assembly 38 has been mounted thereon, may be moved about radially in aligning the gun assembly before flange 44 is welded to assembly collar 46.

A sectional enlargement of the barrel assembly output section 80 is shown in FIGURE 4 where parts similar to those of input section 54 in FIGURE 3, are identified with the same numerals followed by the letter a. For this reason, the description of the helix 30a, its connection with pin 74a within sleeve 70a, the positioning of helix assembly cover 62a, the use of connecting straps 64a, and the construction of cylinder 48a is not believed to be necessary. The mounting of collector assembly 88 through ceramic spacer 92 is an enlargement of the corresponding arrangement in FIGURE 2.

An end View of the barrel assembly output section 80 is shown in FIGURE 5, with parts broken away to better show certain portions. Here there is shown helix 30a positioned between rods 56a, 58a and 60a within helix assembly cover 62a, all positioned within cylinder 48a from which are projected pole pieces 50a. Rod 74 is connected to helix 30a and is spaced from sleeve 70a by ceramic spacer 72a which is not shown in FIGURE 5 but is shown in FIGURE 3. Straps 64a additionally hold the helix 30a in position and connect it to the cylinder 48a.

One of the pole piece assemblies is shown, partly in section, in FIGURE 6 and in perspective in FIGURE 7. Donut-shaped pole pieces 5% and 500 are stamped from magnetic material and are interconnected with a nonmagnetic sleeve 122, such as Monel, for example. These units are copper brazed along the mating edges in vacuumtight relationship. Each pole piece assembly may then be checked for reliability before becoming part of the cylinder assembly. As the pole pieces are then assembled and welded along their peripheries, after being positioned in alignment, they may again be inspected before proceeding with the assembly. In this manner each part is checked for perfection and those parts having the flaws therein may be removed and discarded completely before the more expensive unit has been assembled. By thus checking each individual unit before assembling with the next unit, greater reliability is achieved at less cost.

The pole pieces and their assemblies become an integral part of the vacuum envelope, permitting a heavier power-carrying capability in the output. They are more easily assembled, using the severed helix technique, and permit easier collector assembly alignment. They also permit continuous vacuum pumping of the tube during its operation. In this manner the traveling-wave tube comprising the present invention is easier and more reliably constructed and is more dependable over a longer lifetime of the tube.

Having thus described a preferred embodiment, it is to be understood that modifications will readily become apparent to those skilled in the art and that such modifications are intended to be encompassed by the present invention as set forth in the following claims.

What is claimed is:

1. A traveling-wave tube including (a) an elongated evacuated envelope,

(b) an electron gun at one end of said envelope and serving to form an electron beam,

(c) a collector at the other end of said envelope and serving to intercept said beam,

(d) a helical conductor disposed axially within said envelope,

(e) coupling means for coupling electrical energy onto and off said helical conductor, said coupling means comprising hollow cylindrical metallic portions, ceramic spacers bonded to the outer ends of said coupling means and forming hermetic seals therewith, conductors extending through said seals and connected to the ends of the helical conductors,

(f) said evacuated envelope comprising a plurality of pole piece assemblies, each pole piece assembly comprising a nonmagnetic sleeve brazed between a pair of donut-shaped magnetic disks, the disks of adjacent pole piece assemblies being bonded to each other in vacuum-tight relationship, and

(g) magnets positioned over said sleeves and between said disks.

2. A traveling-wave tube comprising (a) a gun assembly, a slow wave device, and

(b) a collector assembly,

(c) said slow wave device comprising an assembly input section and an assembly output section, said input section having a gun alignment flange positionable thereon for bonding thereto,

(d) said gun assembly being mounted on said alignment flange,

(e) said input section having an input coupler and an axial wave-retarding conductor connected to said input coupler, said input section including an envelope cylinder comprising a plurality of pole piece assemblies welded together in a vacuum-tight relationship,

(f) said pole piece assemblies each comprising a nonmagnetic sleeve having donut-shaped disks separated thereby, adjacent disks of adjacent pole piece assemblies being welded to each other about the periphery thereof,

(g) said assembly output section being constructed in a manner silimar to said input section and having an insulating spacer ring connected thereto, said collector assembly being attached to said spacer ring.

3. A traveling-wave tube comprising the gun assembly,

a slow wave device, and a collector assembly,

(a) said slow wave device comprising an assembly input section and an assembly output section, an axial wave-retarding conductor mounted in each of said sections, said sections being joined together in vacuum-tight relationship,

(b) said input section having an input coupler connected to said wave-retarding conductor associated therewith for transmission of energy thereto,

(c) said output section having an output coupler connected to said Wave-retarding conductor associated therewith for the transmission of energy therefrom, and

(d) an insulating spacer ring interconnecting said collector assembly with said output section,

(e) each of said input and output sections comprising cylinders made up of a plurality of nonmagnetic sleeves having annular magnetic pole pieces extending outwardly therefrom adjacent magnetic pole pieces being joined to each other in vacuum-tight relationship at the outer peripheries thereof.

4. A traveling-wave tube comprising (a) a gun assembly,

(b) a slow wave device, I

(c) said gun assembly having a gun alignment flange for aligning said assembly on one end of said slow wave device,

((1) a collector assembly mounted on the other end of said slow Wave device, and

(e) a vacuum pump,

(f) said collector assembly having a collector plug with an ofiset passageway therethrough said passageway communicating between said collector assembly and said vacuum pump, and a blocking Window comprising an apertured metallic plate between said collector plug and said slow Wave device to trap secondary electrons emitted from said collector plug.

References Cited by the Examiner UNITED STATES PATENTS 2,789,246 4/1957 Wang 3153.6 X 2,843,775 7/1958 Yasuda 3153.5 X 2,849,651 8/1958 Robertson 3153.5 X 2,891,190 6/1959 Cohn 31539.3 X 2,922,919 1/1960 Brtick 315-36 2,964,670 12/1960 Bliss 315-35 3,043,984 7/1962 Stephenson 31539.3 X 3,088,105 4/1963 Beam 3153.6 X 3,172,004 3/1965 VonGutfeld et al. 3153.5 X 3,173,048 3/1965 Chun 315-39.71 X 3,206,635 9/1965 Phillips 3153.5 X

HERMAN KARL SAALBACH, Primary Examiner.

R. D. COHN, Assistant Examiner.

Claims (2)

1. A TRAVELING-WAVE TUBE INCLUDING (A) AN ELONGATED EVACUATED ENVELOPE, (B) AN ELECTRONGUN AT ONE END OF SAID ENVELOPE AND SERVING TO FORM AN ELECTRON BEAM, (C) A COLLECTOR AT THE OTHER END OF SAID ENVELOPE AND SERVING TO INTERCEPT SAID BEAM, (D) A HELICAL CONDUCTOR DISPOSED AXIALLY WITHIN SAID ENVELOPE, (E) COUPLING MEANS FOR COUPLING ELECTRICAL ENERGY ONTO AND OFF SAID HELICAL CONDUCTOR, SAID COUPLING MEANS COMPRISING HOLLOW CYLINDRICAL METALLIC PORTIONS, CERAMIC SPACERS BONDED TO THE OUTER ENDS OF SAID COUPLING MEANS AND FORMING HERMETIC SEALS THEREWITH, CONDUCTORS EXTENDING THROUGH SAID SEALS AND CONNECTED TO THE ENDS OF THE HELICAL CONDUCTORS, (F) SAID EVACUATED ENVELOPE COMPRISING A PLURALITY OF POLE PIECE ASSEMBLIES, EACH POLE PIECE ASSEMBLY COMPRISING A NONMAGNETIC SLEEVE BRAZED BETWEEN A PAIR OF DONUT-SHAPED MAGNETIC DISKS, THE DISKS OF ADJACENT POLE PIECE ASSEMBLIES BEING BONDED TO EACH OTHER IN VACUUM-TIGHT RELATIONSHIP, AND (G) MAGNETS POSITIONED OVER SAID SLEEVES AND BETWEEN SAID DISKS.

4. A TRAVELING-WAVE TUBE COMPRISING (A) A GUN ASSEMBLY, (B) A SLOW WAVE DEVICE, (C) SAID GUN ASSEMBLY HAVING A GUN ALIGNMENT FLANGE FOR ALIGNING SAID ASSEMBLY ON ONE END OF SAID SLOW WAVE DEVICE, (D) A COLLECTOR ASSEMBLY MOUNTED ON THE OTHER END OF SAID SLOW WAVE DEVICE, AND (E) A VACUUM PUMP, (F) SAID COLLECTOR ASSEMBLY HAVING A COLLECTOR PLUG WITH AN OFFSET PASSAGEWAY THERETHROUGH SAID PASSAGEWAY COMMUNICATING BETWEEN SAID COLLECTOR ASSEMBLY AND SAID VACUUM PUMP, AND A BLOCKING WINDOW COMPRISING AN APERTURED METALLIC PLATE BETWEEN SAID COLLECTOR PLUG AND SAID SLOW WAVE DEVICE TO TRAP SECONDARY ELECTRONS EMITTED FROM SAID COLLECTOR PLUG.

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